Ground motion selection for seismic risk analysis of civil infrastructure - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 79

(denoted by EDP ) is computed. The second approach, referred to as an
'uncoupled' approach (Fig. 4.1b) treats the same problem in two (or pos-
sibly more) parts by introducing a conceptual boundary between the
domains of (i) earthquake rupture and wave propagation; and (ii) engi-
neering response of the local soil and structure. This uncoupled approach
has numerous benefi ts, elaborated upon by Bradley (2012a); the most
important of which is the ability to use different methodologies for each
task. In particular, it may be impractical to perform earthquake rupture
and wave propagation simulations for the problem under consideration
due to a lack of expertise, input information (i.e. fault rupture details as
well as seismic velocity structure of the propagation medium), and the
perceived limitations of such models (often, the adequate simulation of
high-frequency ground motion). Consequently, (simple) empirical ground
motion prediction equations (GMPEs) are often used to provide the dis-
tribution of various ground motion intensity measures (represented by a
intensity measure vector, IM ) at the site of interest (e.g. peak ground
acceleration). Most importantly, however, such GMPEs provide only the
distribution of ground motion intensity measures, but not ground motion
time histories. Hence, in such cases the problem becomes how to select
ground motion time histories based on the obtained distributions of
ground motion intensity measures.
4.2.2 Emphasis on probabilistic seismic hazard -
consistent ground motions
Ground motions are typically selected on the basis of either deterministic
or probabilistic seismic hazard analysis (DSHA and PSHA, respectively)
(Bommer, 2002). For example, ground motions may be desired to represent
the controlling earthquake obtained from DSHA, or to represent the
ground motion hazard for one or more exceedance probabilities obtained
from PSHA. While it is the author's opinion that assessing the seismic per-
formance of structures under deterministic and probabilistic hazard analy-
ses provide different information and are complementary, the predominant
use of PSHA in seismic design codes has resulted in PSHA - consistent
ground motions being predominantly desired. The desire to obtain such
ground motions is complicated by the fact that: (i) PSHA combines all the
potential seismic sources which constitute a hazard at the site of interest,
and hence the seismic hazard for a given exceedance probability is due to
more than a single seismic source, and (ii) the ground motions at the site,
for the exceedance probability considered, are not median motions expected
if the seismic source was to rupture, but are a function of the features of
the various seismic source and exceedance probability considered. The
complexities entailed from the above two points make the selection of